The present invention relates to a digital broadcasting receiver for receiving modulation waves digitally modulated by a plurality of modulation methods, multiplexed in a time axis to be transmitted, and having different necessary C/N (a ratio of carrier power to noise power) values.
A hierarchical transmission method is known by which digital waves modulated by a plurality of modulation methods and having different necessary C/N values, such as 8PSK modulated waves, QPSK modulated waves, and BPSK modulated waves, are combined in a time axis and repetitively transmitted one frame after another. A digital broadcasting receiver for receiving digitally modulated waves transmitted through such a hierarchical transmission method is provided with an automatic frequency control circuit for reproducing a carrier because the center frequency of a desired reception signal has a deviation of about xc2x11.5 MHz from a rated frequency.
The automatic frequency control circuit (hereinafter simply called an AFC circuit) for reproducing a carrier of a digital broadcasting receiver for receiving a digitally modulated wave transmitted by the hierarchical transmission method, performs a frequency scanning in a range (capture range) the demodulator can reproduce the carrier even in the case of a worst reception C/N, when the carrier is captured, detects that the carrier reproduction is locked, and thereafter stops the frequency scanning in response to this detection output.
However, the scanning step width of the AFC circuit of a conventional digital broadcasting receiver is narrow so that it takes a time for the carrier reproduction to be locked. The time while the frequency scanning is executed becomes long.
The present invention aims at providing a digital broadcasting receiver capable of quickly reproducing a carrier and capturing a desired signal at high speed.
The invention provides a digital broadcasting receiver having an automatic frequency control circuit used for carrier reproduction for receiving a hierarchical digital modulated wave, the digital broadcasting receiver comprising: phase error detecting means for detecting a phase error voltage in accordance with a demodulation output obtained by demodulating the modulatied wave during a predetermined section in a header section; error frequency calculating means for calculating an error frequency between a desired reception frequency and a reproduction carrier frequency in accordance with the detected phase error voltage; polarity calculating means for calculating a polarity of the error frequency in accordance with the detected phase error voltage; and converting means for converting the detected error frequency having the calculated polarity into a step frequency width for automatic frequency control, wherein the reproduction carrier frequency is scanned at the converted step frequency width until a frame sync is established after the frame sync is detected.
According to the digital broadcasting receiver of this invention, after the frame sync is detected, a phase error voltage is detected in accordance with a demodulation output obtained by demodulating the modulated wave during a predetermined section in a header section. An error frequency between a desired reception frequency and a reproduction carrier frequency is calculated in accordance with the detected phase error voltage. A polarity of the error frequency is calculated in accordance with the detected phase error voltage. The detected error frequency having the calculated polarity is converted into a step frequency width for automatic frequency control. The reproduction carrier frequency is scanned at the converted step frequency width until the frame sync is established. Since the frequency scanning is executed at the step frequency width corresponding to the error frequency until the frame sync is established after it is detected, the carrier can be reproduced quickly and the desired signal can be captured at high speed.
The digital broadcasting receiver of this invention further comprises a tracking circuit for generating a tracking signal in accordance with the phase error voltage, to thereby make the reproduction carrier frequency follow a change in the desired reception frequency in accordance with the tracking signal, after the frame sync is established.
According to the digital broadcasting receiver of this invention, after the frame sync is established, the tracking signal output from the tracking circuit makes the carrier frequency follow the change in the desired reception frequency so that the frame sync state can be maintained.